Preparation, characterization and sintering of yttrium-doped ThO2 for oxygen sensors applications

• Th1-xYxO2-x/2 ceramics were successfully prepared from oxalate precursors.
• Precursors and final oxides were extensively characterized.
• Sintering conditions to achieve complete densification of the samples were investigated.
• First evaluation of the electrical conductivity was undertaken by impedance spectroscopy.

The preparation of Th1-xYxO2-x/2 ceramics, to be used as electrolyte in oxygen sensors for sodium-cooled nuclear reactors, was successfully undertaken from oxalate precursors. Such method was found to provide quantitative precipitation of the cations into (Th,Y)(C2O4)2·2H2O solid solutions up to x = 0.15 while a polyphase system was obtained for x = 0.22. The corresponding oxides were obtained through heat treatment in air at 500 °C and characterized by the means of PXRD, SEM and statistical X-EDS measurements. The conditions for the densification of Th1-xYxO2-x/2 ceramics were further determined by dilatometry (T = 1575 °C, t = 8 h) resulting in densification rates up to 99%. Finally, a first estimation of the electrical properties of the solids was undertaken by impedance spectroscopy. Electrical conductivity was found to increase linearly with the incorporation of Y3+ content while the associated values of activation energy decreased, with a minimum value of 1.1 eV for Th0.85Y0.15O1.925.

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